It has long been known that hydrophilic coatings with low friction (coefficient of friction of 0.3 or less) are useful for a variety of medical devices such as catheters, catheter introducers and the like. When low friction surfaces are used, such devices when introduced into the body slide easily within arteries, veins, cannula and other body orifices and passageways. There have been a wide variety of methods used to provide the surfaces desired. In some cases the material of the catheter or medical device is formed of a material having good anti-friction properties such as teflon or other plastics which tend to avoid abrasion with the body. However, in many cases a selection of materials does not provide the anti slip properties desired in conjunction with other desirable properties for the particular medical device.
The art has recognized that polymer surfaces can be provided with hydrophilic coatings formed from combinations of isocyanate, polyurethane and polyvinyl pyrrolidone. Others have suggested applying solutions of poly(ethylene oxide) with isocyanate and/or polyurethane in multi step operations. Often coatings thus formed can lack good adherence to a substrate in combination with high-slip properties. For example, U.S. Pat. Nos. 4,459,317 and 4,487,808 to Lambert disclosed medical devices having hydrophilic coatings formed from an isocyanate layer overcoated with a poly(ethylene oxide) layer. However, such coatings appear to be of polyurea materials formed from a first solution of an isocyanate being applied to a base with a solvent evaporated, followed by a second solution application of poly(ethylene oxide) in turn followed by evaporation of the solvent. Cure is effected by baking in the presence of moisture, thus producing a polyurea. This type of application appears to provide polyurea materials which do not have the tenacity of the coatings of the present inventions. The multistep procedure makes it difficult to tailor properties and values of the final coatings. The coatings of the present invention are the result of polyurethane linkages in combination with an association of poly(ethylene oxide). The use of a one dip process and formation of polyurethane has been found particularly useful to provide low friction coatings which are abrasion resistant in the body, hydrophilic and lubricious.